Ink-jet printing is a non-impact printing process in which droplets of ink are deposited on print media, such as paper, transparency film, or textiles. Low cost and high quality of output, combined with relatively noise-free operation, have made ink-jet printers a popular alternative to other types of printers used with computers. Essentially, ink-jet printing involves the ejection of fine droplets of ink onto print media in response to electrical signals generated by a microprocessor.
There are two common means currently available for achieving ink droplet ejection in ink-jet printing: thermally and piezoelectrically. In thermal ink-jet printing, the energy for drop ejection is generated by electrically-heated resistor elements, which heat up rapidly in response to electrical signals from a microprocessor to create a vapor bubble, resulting in the expulsion of ink through orifices associated with the resistor elements. In piezoelectric ink-jet printing, the ink droplets are ejected due to the vibrations of piezoelectric crystals, again, in response to electrical signals generated by the microprocessor. The ejection of ink droplets in a particular order forms alphanumeric characters, area fills, and other patterns on the print medium.
Many inks that are described for use in ink-jet printing are associated with non-thermal ink-jet printing, such as piezoelectric ink-jet printing. Inks suitably employed in such non-thermal applications often cannot be used in thermal ink-jet printing due to the effect of heating on the ink composition.
In commercially-available thermal ink-jet color printers, such as a DeskJet.RTM. printer available from Hewlett-Packard Company, a color spectrum is achieved by combining cyan, magenta, and yellow inks in various proportions. Ink-jet inks are mostly available as dye-based compositions, although a number of black pigment-based ink-jet inks are also available. Thus, cyan, magenta, and yellow inks typically derive their hues from cyan, magenta, and yellow or pigments, and/or macromolecular complexes, respectively. (A macromolecular complex, or MMC, is formed by suitable chemical modification of the pigment surface so as to render the pigment essentially totally water-soluble.) The particular set of inks, each comprising one or more vehicle components and one or more colorants (dyes or pigments or MMCs), constitutes a so-called "ink set". Color printers typically employ a four-pen set containing cyan, magenta, and yellow inks as well as a black ink, which is typically used for printing text.
The dye-based color ink-jet inks are typically formulated by dissolving dye in an aqueous-based ink vehicle. The dyes employed in ink-jet ink compositions are often in the form of dye salts made of a dye anion and a cation such as sodium, lithium, tetramethylammonium, etc. These dyes are designed to form solids in the target paper substrate by absorption into paper media by at least two mechanisms. In one mechanism the dye is wicked into the paper and absorbed onto active sites of the paper fiber. There is another mechanism operating in which the ink vehicle evaporates, or is wicked away from the dye, leaving solid dye on the paper fibers.
The pigment-based color ink-jet inks are typically formulated by forming a dispersion of the pigment in an aqueous-based vehicle, employing a dispersing agent. Alternatively, the pigment may be chemically treated in some fashion such that it essentially acts like a macromolecular complex, described above. In yet another approach, a microemulsion may be formed by combining a pigment, a macromolecular complex, a water-soluble dye or water-insoluble dye, with a surfactant and water.
Many of the components used in ink-jet inks, whether the colorant is a dye or a pigment or an MMC, are reactive with one or more of the pen components (e.g., resistor pad, nozzle plate, firing chamber material, and the like), which, over time, causes degradation of the component and ultimately of pen performance. Specific components that may react include water and solvents, such as organic compounds, used in the vehicle of the ink.
Further, interaction between the ink-jet ink solvents and the print medium (e.g., paper) can result in cockle and curling problems of the paper. While solutions to these problems have been effective, it is preferable to avoid the problem altogether.
Thus, there is a need for a vehicle component that solves, or at least alleviates, the foregoing problems. The manner of achieving these sometimes conflicting characteristics must be easily implemented and cost-effective.